The digital era has given camera buyers abundant new choices. But changes that came with higher-end models called digital SLRs have also imposed new lens complexities and compatibility issues buyers hadn't bargained for.

On the one hand, the engineers behind single-lens reflex cameras, now unleashed from the constraints of 35mm film, can match the image sensors at the heart of digital SLRs to different cost and engineering priorities. On the other hand, because the size of those sensors therefore varies, the same type of lens often produces different results when comparing one digital SLR to another--or to 35mm film SLRs. In one situation, lenses are not just different, but actually incompatible as well.

Consumers, who have shown a strong appetite for digital SLRs and the cameras' accompanying high-quality images, are grasping the new rules. But no one denies there's a learning curve to demystify the details.

Take the case of Jesse Warren, an English teacher and avid photo hobbyist in Shenzhen, China. He concluded that, with lens compatibility issues in mind, he'd be wise to avoid Canon EF-S lenses that work only on small-sensor SLRs and to stick to the EF models that follow the older standard.

"After asking around for a few weeks, I came to fully understand the details of lens focal length and compatibility," he said. "I am very concerned, which is why I will probably invest in EF lenses."

Manufacturers are unrepentant about the newly fluid situation. "Standards always lead to something that makes life easier for the consumers, but it also limits creativity" for camera designers, said Darin Pepple, marketing manager for Fujifilm. "You have to weigh both sides."

On traditional film SLR cameras, a lens with a 50mm focal length closely approximates the optics of a human eye. But smaller sensors on most digital SLRs mean that a 50mm lens has a narrower field of view, which leads to light from a smaller angle hitting the sensor (). As a result, for example, the image of a car that shows completely on a 35mm film SLR might be missing the bumpers when viewed with a digital SLR using the same lens.

A conversion factor is used to describe new-era cameras in old-era terms.

For example, on a Nikon or Fujifilm, a 50mm lens shows the same field of view as a 75mm lens on a film SLR and therefore has a 1.5x conversion factor. On an Olympus or Panasonic, a 50mm lens works like an old-school 100mm lens. And for digital SLR market leader Canon, the equivalent is 80mm for consumer models, 65mm for its midrange line and an unchanged 50mm for top-of-the-line models with "full-frame" sensors.

The issue isn't likely to fluster experienced photographers. But now that digital SLRs cost less than $650--not much more than high-end point-and-shoot cameras--a new generation of less sophisticated buyers is arriving in the market.

Electronics manufacturing issues triggered the change. Although full-frame sensors preserve compatibility with film SLR cameras and produce cleaner images, they're more expensive and consume more battery power. Canon must make full-frame sensors by joining several smaller ones.

"You definitely have an entirely disruptive situation as the silicon guys drive the technology," said analyst Jeff Clark of Current Analysis.

Even as computing technology remakes the camera business and film becomes a relic, the film frame standard endures as a reference point to compare photographic equipment. The 35mm camera standard prevails for describing the lenses even of simple point-and-shoot cameras that lack interchangeable lenses.

New wrinkles for old standard
For decades, photography fans preferred 35mm film SLR cameras for their balance of size, image quality, film cost and the attraction of interchangeable lenses. By attaching different lenses to the same camera, people can photograph everything from wide crowd pictures to distant birds. Enthusiasts and professionals accumulated lens collections to span the range and fit special circumstances.

The 35mm label derives from the size of the film, 35mm wide with a negative measuring 36mm by 24mm. SLR refers to a reflex mirror that reflects light from the lens directly into the viewfinder, then snaps out of the way to expose the film. The design means the photographer sees the same image that appears on the image sensor, even when employing different lenses.

The narrower field of view on many digital SLRs boosts telephoto lenses, those with long focal lengths. For example, a 200mm lens on a film SLR works like a 300mm lens on a Nikon digital SLR or a 320mm lens on a consumer-level Canon competitor.

"The 1.6x factor on the focal length has, for my main subject of railways, been a bonus," said Chris Millner, an English photo buff and deputy editor of The Railway Magazine.

About the author

Stephen Shankland has been a reporter at CNET since 1998 and covers browsers, Web development, digital photography and new technology. In the past he has been CNET's beat reporter for Google, Yahoo, Linux, open-source software, servers and supercomputers. He has a soft spot in his heart for standards groups and I/O interfaces.
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